1. Field of the Invention
The present invention relates to a communication network of a microcomputer-assisted controller including a serial communication device.
2. Related Background Art
Nowadays, measuring and observing devices and many other controllers perform a variety of control operations based on microcomputers. Operations by the user are simplified and facilitated by automatically adjusting respective units of the devices when effecting the measurements, observations and control. In a complicated device, a simple one-chip microcomputer is incorporated into every unit of the device, and each unit is automatically adjusted. At the same time, each of the microcomputers is controlled by a personal computer, or alternatively, as increasingly practiced, the device is operated by receiving and transferring the data between the microcomputers.
As explained above, in the controller having the units each incorporating a central processing unit (CPU) known as a microcomputer, when receiving and the transferring the data from and to other units, in the great majority cases, serial communications are conducted by use of an RS232C port. In this type of serial communications, as illustrated in FIG. 1, there is a one-to-one correspondence between the input and output terminals of two devices A, B for receiving and transferring the data. More particularly, an RXD terminal serving as an input terminal of one device is connected to a TXD terminal serving as an output terminal of the other device. A plurality of sets of the data input and output terminals are thus needed for connecting a single device to a plurality of devices.
In the arrangement shown in FIG. 2, for example, an RXD1 terminal as a data input terminal of the first device A is connected to a TXD1 terminal as a first data output terminal of the second device B. At the same time, the TXD1 terminal defined as a data output terminal of the first device A is connected to the RXD1 terminal defined as a first data input terminal of the second device B. This arrangement allows transferring and receiving the data between the first and second devices A, B. Further, the data are received and transferred between the second device and a third device C by connecting an RXD2 terminal defined as a second data input terminal of the second device B and the TXD1 terminal defined as a data output terminal of the third device C, and connecting the TXD2 terminal defined as a second data output terminal of the second device B and the RXD1 terminal defined as a data input terminal of the third device C. In this way, the pairs of data input and output terminals are connected in order to establish communications.
On the other hand, parallel communications through a GPIB (General Purpose Interface Bus) are conducted between devices in some cases. The parallel communications involve the use of a plurality of control lines in addition to a data bus. Then, the devices exclusive of two specified devices are electrically disconnected from the data bus, and the data are transferred between these two specified devices.
Nowadays, there are increasingly demands for improving the function of whole systems and making the working mode changeable according to the application by adding an optional device to the system constructed of the plurality of devices connected to each other. It is also required that the operation be automated by having a built-in CPU and that the data be transferred to and received from other devices of the system. Hence, the added optional device also has to incorporate a serial communications function.
The serial communications enable the data to be transferred between the devices simply by use of the RS232C interface. It is, however, required that the respective devices be connected in the one-to-one correspondence. In the case of adding a device to an existing system, the programs of the CPUs incorporated into the devices constituting the existing system are changed, and the conventional device and the device to be added have to be individually connected. This makes it difficult to add a new device having the built-in CPU to the system.
In a system using parallel communications, an optional device is connected to the data bus as well as to the control bus, and it is therefore easy to expand the system by adding devices. However, a control circuit dedicated to the parallel communications is needed. The majority of boards, each known as a one-chip microcomputer, generally employed at present do not incorporate a parallel communications function. Accordingly, in order to assemble the system, the device to which a dedicated I/O port is added beforehand has to be manufactured, so that manufacturing the device and its respective units is complicated and expensive.